1. Field of the Invention
This invention relates to the novel use of flame retardant additives in polymers. More particularly, this invention relates to the use of halogenated imide-containing polyols as flame retardants in thermoplastic polymeric compositions.
2. Description of the Prior Art
The two major types of polymers are the thermosets and the thermoplastics. The thermoset polymers consist of those plastics which when subjected to heat, will normally become infusible or insoluble, and as such cannot be remelted. They have elaborately cross-linked three-dimensional structures and are used for plastics, elastomers, coatings and adhesives.
In contrast to the thermoset polymers, most thermoplastic polymers can be made to soften and take a new shape by the application of heat and pressure. Thermoplastics consist of long-chain molecules often without any branching (e.g., high density polyethylene). Even if there is branching (e.g., low density polyethylene) the polymer may still be two dimensional. Thermoplastic polymers consist of those plastics which normally are rigid at operating temperatures, but can be remelted and reprocessed. They include polyethylene, polypropylene, polystyrene, polyvinyl-chloride, acrylonitrile-butadiene-styrene (ABS), nylon, and the like.
The problem of the flammability of polymer compositions has received considerable attention. A variety of compounds exist that provide satisfactory flame resistance, smoke suppression and self-extinguishing properties. These conventional flame retarding agents are either reactive or additive. The reactive compounds are incorporated into the structure or backbone of the polymer. In contrast, additive flame retardants are only physically incorporated into the polymerized product. Additive compounds typically include tris(chloropropyl)phosphate and aluminum trihydrate.
Co-pending application Ser. No. 303,055 filed on Sept. 17, 1981 is directed to the use of halogenated imide-containing polyols and corresponding ethers as reactive flame retardants for polyurethanes. These same halogenated imide-containing polyols have now been found to be effective additive flame retardants for a variety of thermoplastic polymeric compositions.
It is known to use polyol esters of tetrabromophthalic anhydride as a reactive component in the preparation of flame retardant polyurethanes. U.S. Pat. No. 3,642,646 discloses polyol compositions useful in preparing rigid foam compositions. These polyols comprise the reaction adducts of polyfunctional aromatic carboxylic acid anhydrides or chlorendic anhydride and polyether polyols. It specifically teaches the use of half esters based on a polyol and tetrabromophthalic anhydride.
U.S. Pat. No. 3,585,185 discloses a process for preparing ester-containing polyols by the reaction of alkylene oxide condensates of organic compounds having at least two active hydrogen atoms with a halogen-containing organic acid anhydride and an alkylene oxide.
U.S. Pat. No. 3,454,530 teaches the use of polyols useful in the preparation of rigid polyurethane foams. These polyols are prepared by the reaction of a di- or tri-alkanolamine with a cyclic anhydride of an organic dicarboxylic acid and a lower alkylene oxide.
Canadian Pat. No. 993,451 discloses halogen-substituted aromatic amide-ester polyols and their use in a flame retardant flexible polyurethane foam.
U.S. Pat. No. 3,676,376 teaches the use of polyester polyols based on tetrabromophthalic anhydride, an aliphatic dicarboxylic acid, a polyol and an aliphatic diol.
U.S. Pat. No. 3,989,653 teaches the preparation of diesters of tetrabromophthalic anhydride by the reaction product of tetrabromophthalic anhydride and a polyhydroxy compound containing at least three hydroxyl groups.
Spatz et al in "Industrial and Engineering Chemical Product Research and Development," Vol. 8, No. 4, pages 397-8 (1969), teach the use of N-(2-hydroxyethyl)tetrabromophthalimide as a flame retardant in some thermoset polymeric compositions.
None of the references are directed to the halogenated imide-containing polyols and ethers of the present invention. These prior art flame retardants are limited in application to thermoset compositions or polyurethanes. In addition, they are reactive and thus are incorporated into the structure of the polymer itself.
U.S. Pat. Nos. 3,565,812, 3,639,541, and 3,639,542 are directed to the preparation of halogen-containing organic acid anhydrides based on ester- and phosphorus-containing polyols.
The prior art flame retardants are esters. They are intended for use in polyurethane compositions. They have lower hydrolytic and thermal stability than the flame retardant mixture in the present invention. In addition, production of the present halogenated imide-containing polyol and ether do not require the use of an alkylene oxide such as propylene oxide. This is advantageous because lower alkylene oxides are toxic, explosive and require the use of pressure equipment.
The flame retardants of the present invention are additive flame retardants and are dispersed throughout the polymer matrix. Traditionally, a flame retardant additive is incorporated into the thermoplastic polymeric composition after the thermoplastic polymer is completely formed. Under heat and pressure the thermoplastic polymer is melted and the flame retardant additive is blended in. Some state of the art additive flame retardants remain in solid form throughout this blending process. Therefore, an uneven dispersion of flame retardant into the final product frequently results. It has recently been discovered that the halogenated imide-containing polyols and corresponding ethers of the present invention melt during this blending step. Thus, a more even dispersion of flame retardant throughout the thermoplastic polymer matrix is achieved. This improved dispersion of the flame retardant additive allows for more efficient flame retardance and greater retention of useful polymer physical properties.